1. Field of the Invention
The present invention relates to an image processing apparatus for storing image data in a memory, reading stored image data from a memory, and generating print data (i.e., data for printing out an image on paper such as in a printer, copier, facsimile machine and the like). The present invention specifically relates to an apparatus for processing image data used for simultaneous parallel printing in a plurality of colors such as yellow (Y), magenta (M), cyan (C), and black (Bk).
2. Description of the Related Art
In color image forming apparatuses such as color printers, color copiers, color facsimile machines and the like, since full color images are formed by overlaying images of each print color Y, M, C, and Bk, the image data of each print color must be output to the printhead with optimum timing so as to not produce dislocation of the images of the various print colors. For this reason the image data of each print color are temporarily stored in a frame memory beforehand, so as to be controllably read out with optimum timing.
In these color image forming apparatuses, the processing of the image data of each print color Y, M, C, Bk must be accomplished via simultaneous parallel execution in order to be able to form the image in a short time. For this reason the image data of each print color are simultaneously stored in a frame memory beforehand, so as to allow the data to be read out in parallel via an optimum timing.
In the image forming apparatus, the memory for storing the image data must be used efficiently in order to increase the speed of image formation and/or colorize the image, and/or reduce cost. That is, although cost can be reduced by reducing memory capacity, the formation of a plurality of images at high speed becomes difficult due to the reduced number of images that can be stored simultaneously. Furthermore, when memory capacity is too small and the image data of the four colors Y, M, C, and Bk cannot be stored simultaneously, the color image formation speed is slowed because the images of the four colors Y, M, C, Bk cannot be formed simultaneously.
Image data compression methods are methods for storing a relatively large amount of image data in a relatively small capacity memory. Various image data compression methods are known, but from the perspective of image editing (rotation, trimming, masking and the like), there are compression methods which allow editing in a compressed state, and methods which do not allow editing in a compressed state. It is desirable to allow editing in a compressed state since typical image processing apparatuses expand the image data read out from the frame memory and output these data to a printhead, and do not have a dedicated editing process circuit in the latter part of the expansion circuit. The ability to edit or the lack thereof differs according to the target editing method.